Strange problem!!

1.Sorry for my english
2.I have a perfect setup on ubuntu breeze system
my dns on godday grupaprop.net my server name is omaxserver omaxserver.xxxxxxx.net, all functions of server work perfectly lasts months smtp, pop3, etc... but now can't recive mails, when some body try to send me a mail the postfix return this error

3.
This is the Postfix program at host omaxserver.xxxxxx.net.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to <postmaster>

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

I was install thi programs for prevent attacks, I had executed the chkrootkit and rkhunter and it hadn't detected nothing, i had change my ip for try to repair that problem but now the error change for this:

This is the Postfix program at host omaxserver.grupaprop.net.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to <postmaster>

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

Dynamic IP Space (LAN, Cable, DSL & Dial Ups)
Netblock: 85.52.0.0/14 (85.52.0.0-85.55.255.255)
Record Created: Sun May 14 11:47:30 2006 GMT
Record Updated: Sun May 14 11:47:30 2006 GMT
Additional Information: Dynamic/Generic IP/rDNS address, use your ISPs mail server or get rDNS set to indicate static assignment.
Currently active and flagged to be published in DNS
If you wish to request a delisting please do so through the Support System.

Thanks for your support, I recently reinstall all server with ubuntu 6.06 dapper on amd64 and I change my internet conection, all run ok!! if problem return I will use another email server for relaying my dominds.